Lateral strip control apparatus

ABSTRACT

Apparatus for transversely moving and positioning a segment of a flexible magnetizeable strip to permit access to a specified one of a plurality of data tracks thereon by a data transducer. In a preferred embodiment, the transducer is mounted in a rotating drum partially encircled by the strip and the strip segment is transversely moved by two pairs of parallel bars or cylinders through which the strip runs. In each pair, the strip partially encircles each bar in opposite directions by passing between them. By angling the pairs of bars with respect to the strip itself the portion of the strip between the pairs of bars may be caused to move to desired transverse positions.

United States Patent [191 Larson [451 Nov. 20, 1973 [73] Assignee: Control Data Corporation,

Minneapolis, Minn.

[22] Filed: June 7, 1972 [21] Appl. No.: 260,602

Dale Larson, Minneapolis, Minn.

[52] US. Cl. 179/1002 T, 226/22 [51] Int. Cl.. Gllb 15/43, G1 1b 15/60, G1 lb 27/22 [58] Field of Search 226/24, 27, 28, 180,

226/184, 185, 189, 190, 199, 15-19, 2l22; 179/1002 MD, 100.2 T, 100.2 CA, 100.1

3,024,955 3/1962 Powers, Jr. 226/22 2,716,026 8/1955 Axworthy 226/22 2,797,091 6/1957 Fife 226/22 Kurz 226/18 Fife 226/180 Primary ExaminerVincent P. Canney Assistant ExaminerAlfred l-l. Eddleman Attorney-Joseph A. Genovese et al.

[57] ABSTRACT Apparatus for transversely moving and positioning a segment of a flexible magnetizeable strip to permit access to a specified one of a plurality of data tracks thereon by a data transducer. in a preferred embodiment, the transducer is mounted in a rotating drum partially encircled by the strip and the strip segment is transversely moved by two pairs of parallel bars or cylinders through which the strip runs. In each pair, the strip partially encircles each bar in opposite directions by passing between them. By angling the pairs of bars with respect to the strip itself the portion of the strip between the pairs of bars may be caused to move to desired transverse positions.

52 Claims, 12 Drawing Figures PATENTED REV 20 I973 SHEET 2 [IF 5 T T R H 0.0 O M MN MR ww mm a Q. Rum; GE flw nl ME MAI a R 06 OMSN 2 D RD R R OE 0 MN 0 FE FAPS a 2 0.. a 5 5 RW 3 0 a a I R 2 w K. I u m m H F MN L mu L R a 0 D on i R m 2 T E N R O C I VOICE COIL TO LEFT REWIND MOTOR CONTROL SIGNALS DATA PROCESSOR D ATA PATENTEB NOV 20 I975 SHEET Q 0F 5 FIG, 8,

FIG, 10,

2/911 R 2 VOICE COIL SENSOR POSITION CONTROL 302 303 STRIP CONTROL UNIT LATERAL STRIP CONTROL APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention Generally, the field involves apparatus for mass storage of data which is automatically retrievable under computer or other control. To define the field more narrowly, this invention relates to devices having as the storage medium a recording surface such as iron oxide, and transducers for reading and writing information on the surface, which moves relative to the transducers. This definition of the field is probably the most important, since it includes the devices which will be the competitors of this invention in the market place. In-

cluded are disc and drum memories, noted more for their capacity than their access speed although data rates, once the desired physical area is addressed, may be quite high. More narrowly still, the field relates to such devices having a flexible, magnetizeable surface on which the reading and writing occurs.

2. Description of the Prior Art Perhaps the most closely analogous device in the prior art is the magnetic strip file which has been available for some time but never widely used due to its expensive, complicated structure. (See U. S. Pat. No. 2,722,676, Begun, for an example of one strip file apparatus.) Less analogous to this invention, but more familiar, is the ordinary magnetic tape data recorder which usually has a multi-track head reading and writing on a relatively narrow magnetizeable strip.

In the art of prior magnetic strip files, the major objection involved the problem of addressing a plurality of tracks with one head. If a head was included for each track, many slip rings, or alternative means, were needed to transmit the data from the rotating drum to the frame. Alignment problems would still often require slight shifting of the strip. If one head accessed several tracks, problems in shifting the heads relative to the tracks arose. In some designs, the entire strip was shifted. Others shifted the heads themselves. Still other shifted the drum or other element carrying the heads. In each case a relatively large amount of mass had to be accelerated and decelerated causing difficulty in accessing a track quickly and accurately.

SUMMARY OF THE INVENTION The essence of this invention is apparatus which performs the multiple track addressing by shifting the strip relative to the head path more effectively and efficiently than heretofor has been possible. It borrows a technique which has long been used in controlling webs, such as paper, polyethelene film, and cloth. Such devices are described in, among other references, U. S. Pat. Nos. 2,7 l6,026, Axworthy; 2,797,091, Fife; and 3,024,955, Powers. Each of these patents describe variations ofa device common to all of them, a pair of parallel guide rollers over which the web passes in a particular way, viz. between the rollers and partially encircling each. By pivotally shifting the direction of the axis of rotation of the pair of parallel rollers with respect to the direction of motion of the web, the position of the exiting web can be changed with respect to that of the web entering the guide rollers. Alternatively, the rollers may be set at an angle to web motion and the transverse web position varied by varying the distance between the pair of rollers.

This invention utilizes a rotating drum or other means to support a conventional data transducer adja:

cent a recording medium with respect to which the transducer moves. If supported by a drum, the transducer may be embedded within the curved surface of the drum with its transcribing surface facing outwardly therefrom. A flexible strip having a plurality of recording tracks may then be used as the recording medium. The strip partially encircles the drum and is supported by an air bearing interface thereon. As the drum rotates, the circle described by the transcribing surface of the data transducer traces out a data track when adjacent the strip surface encircling the drum. By appropriate selection of the data transducer and its input signals, data may be written onto, read from, or erased from the recording strip. The part of the strip on each side of the drum passes through a set of guide rollers as described above. If both pairs of rollers are pivoted so as to cause the strip section between them to be shifted toward a desired end of the drum, a second track on the strip may be accessed by the data transducer. The shifted portion will remain parallel to the unshifted part, and tension across the width of the strip will be uniform, preventing asymetrical stretching or scalloping of the strip. By accurately measuring the position of the strip on the drum and by coordinating therewith the pivoting of the two pairs of guide rollers, the data transducer may be made to access a plurality of adjacent and closely spaced recording tracks. Various means may be used to tension the strip to keep the strip positioned properly and sufficiently close to the transducer to permit transcription of data.

Many advantageous variations and improvements on this basic device may be made. While the above invention was described in terms of guide rollers, impliedly rotatable, it is actually preferable to substitute for each roller a cylinder or bar having a curved convex surface encircled by the strip and provided with means for creating an air bearing contact between the strip and the guide cylinder surface encircled by the strip. An air bearing interface between the strip and a bar reduces friction to very nearly zero between them. When used in the guide bar assemblies, by merely pivoting each pair of guide bars as described will cause the strip to slip transversely on them and on the drum to allow accessing of a new track without the necessity of moving the strip longitudinally through the guide bar assemblies. The term bar" will be used hereafter to denote both rollers or non-rotating cylinders, partially encircled by the strip.

The strip need not be short, but may be made as long as several thousand feet. The length of strip not in current use may be stored on a pair of take-up spools which can be rotated when it is desirable to present a fresh surface with a new set of tracks for accessing to the drum. Widths up to 60 cm. may be easily accommodated.

Many advantages not heretofore attainable result from the use of the apparatus described. The guide bars may .be hollow, and hence of low mass. Low mass means low acceleration forces when pivoting them. The section of the strip transversely accelerated is also of very low mass. Both the strip and the guide bars move but a short distance, a matter of a very few inches at the most. For all these reasons, a new track may be accessed very rapidly. The conventional method of accessing a new track involves either moving the drum, the heads or the strip ends themselves.

The use of air bearings on the drum and the guide bars allows other important advantages to be realized. Since friction is made very low thereby, frictional hysteresis is very low, resulting in high repeatability of strip positioning. Damage to the strip is minimized by the low friction. It is not necessary to longitudinally pass a portion of the strip through the pairs of guide bars while the guide bars are being pivoted, to permit proper positioning of the strip. The accurate positioning of the strip permits a higher density of tracks per unit width of the strip. Higher density permits more rapid access and storage of a larger amount of data.

Other advantages of the invention will become apparent from the drawings and explanation which follows.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a left side perspective view of a simplified embodiment of the invention.

FIG. 2 is a right side perspective view of a fully useable eembodiment of the invention.

FIG. 3 is a cross-sectional view of the strip position control system of FIG. 2 and a block diagram of the control electronics.

FIG. 4 is a top view of the apparatus of FIG. 2. FIG. 5 is an alternative embodiment of the apparatus, employing a different means of shifting strip position on the drum.

FIG. 6 is a cross-sectional view of the drum surface showing the arrangement of a transducer head.

FIGS. 70 and 7b display the means for creating an air bearing contact between a bar and the strip.

FIGS. 9a and 9b are orthogonal views of the strip passing over a pair of guide bars and display the dimensions which determine the amount of strip offset.

FIG. 8 displays an alternative means for mounting and pivoting a pair of guide bars.

FIG. 10 displays a block diagram of the strip position control system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1 and 2, shown therein is a frame 100 on which, or relative to which, are located all the essential mechanical components of this invention. The outside housing of motor 103 is attached to frame 100. Drum 101, mounted on the output shaft of motor 103 and rotated thereby, may be supported at the right, or free end by a bearing 240 not shown for clarity in FIG. 1. Data transducer head 111 is embedded within and held by drum 101 with its transcribing surface facing outwardly from the surface of drum 101,

the physical relationship being more clearly shown in FIG. 6. The dotted lines labeled 111 in FIG. 2 indicate position of the heads when a plurality of them are employed. Guide bar holders 104a and 104k are pivotably attached to frame 100 by pivots 122a and 122b. Held rigidly with respect to each other by holder 104a are a pair of guide bars 105a and 106a, the surface of each comprising a convexly cylindrical surface. Although plane, i.e., the plane perpendicular to the axis of drum 101, are controlled by solenoids or voice coils 114a and 114b, setting the angular position of assemblies 121a and 1211) respectively. Voice coils 114a and 114k are pivotally attached to frame by members 118a and 1l8b respectively. The surfaces perpendicular to the axis of rotation of holder pivots 122a and 122b must be planes perpendicular to the vertical plane and for convenience. will be referred to as horizontal planes (although those associated with pivot 122a need not be parallel to the apparent horizontal plane of FIGS. 1 and 2 or to those of pivot 122b, and vice versa). Voice coil 114b has a sliding armature 115b attached by pivot 124b to bracket 116b, which is in turn attached to the end of bars and 106b. Thus, movement of armature llSb varies the angular position of bars 105b and 106b with respect to the vertical plane. The position of armature llSb is controlled by voice coil input 119b, shown in FIG. 2 as supplied by control unit 205. A similar arrangement is made for voice coil 114a and the elements associated with it.

Strip 102 is the actual recording medium on which data is transcribed by data transducer head 111. The ends of strip 102 are held with respect to frame 100 by means allowing little or no movement of them perpendicular to the vertical plane while permitting slight extensions of strip 102 to accommodate variations in the length of its path as supports 104a and 104b are pivoted. By allowing slight extension of the strip at least at one end, more uniform tension may be maintained as the length of the path of strip 102 varies. For convenience, strip 102 has parallel edges, is symmetrical, or uniform, in cross section, and is of material of uniform modulus of elasticity, although these conditions are not necessary for operation of.the device. In FIG. I, the holder of the near end of strip 102 comprises a simple clamp or bracket ll3b attached by springs 112 to frame 100. The far end of strip 102 may be rigidly attached to frame 100 by a similar bracket 113a (not visible). Each bracket clamps its end of strip 102 across the entire width of the strip to insure uniform tension across the width, thereby preventing skewing and curling of the strip. FIG. 2 displays an alternative embodiment comprising capstans or spools-208a and 208b on which portions of strip 102 not in current use may be stored pending the need to transcribe data onto surfaces of the strip stored on spools 208a or 208b.

In describing the path of strip 102, it is assumed that strip 102 tension is great enough to form flat surfaces or segments where strip 102 passes between the various bars. Each segment has its own reference number designation. The segment in FIG. 1 closest to the viewer, segment 102b, extends between holder 113b and guide bar l06b. Strip 102 partially encircles the convex cylindrical surface of guide bar 106b, passes between guide bars l05b and 106b forming segment 102a, and partially encircles the convex cylindrical surface of bar 105b. The path of strip 102 further extends from bar 105b and around idler bar b, passing between it and drum 101 and forming strip segment 102d. The part of bar 1 10b encircled by strip 102 is a part of a convex cylindrical surface of bar 110b, whose axis is parallel to that of drum 10. Part of segment 102a of strip 102 encircles drum 101, as shown.

Referring briefly to FIG. 4, strip 102 is seen to pass between drum 101 and idler bar 110a and partially encircle idler bar 1 10a, whose encircled surface is, as with idler 110b, convexly cylindrical with its axis parallel to the axis of drum 101. The strip further extends to form flat segment 102f by partially encircling guide bar 105a, passing between it and guide bar 106a (FIG. 2). It partially encircles bar 106a, and passes over idler bar 202a to takeup spool 208a, forming strip segments 1023, 102k and 102i respectively as shown. Bars 105a, 106a and 202a all have smooth, convexly cylindrical surfaces where encircled by strip 102. Takeup spools 208a and 208b store that portion of strip 102 not containing tracks needed for immediate addressing by heads 111. Idler bars 202a and 20212 are needed when takeup spools such as 208a and 208b are used. Thus, neither idler bar 202a or 20212 are present in the embodiment of FIG. 1.

In the preferred embodiment, strip segments 102b and 102d both are parallel to the horizontal plane associated with guide bar assembly 121b. Similarly, strip segments l02f and 10211 are parallel to the horizontal plane associated with assembly 121a. These constraints are necessary to achieve equal tension across strip 102 as guide bar assemblies 121a and 12111 are pivoted on their respective pivots 122a and l22b (not visible in FIG. 2). The need for idler bars 202a and 202b thus becomes apparent. Taking up and paying out stored lengths of strip 102 on spools 208a and 208b will change the parallel relation of segments 1 02b to 102d and l02f to 102h if these idler bars are not present.

In the apparatus of FIG. 2, the axial or lateral position of strip 102 with respect to head 111 is accurately measured and the measurement is employed in feedback apparatus to precisely position strip 102 on drum Strip position is determined by position of strip edge sensor 220 which is carried by arm 218, slidably attached to and moved by voice coil 219 in turn attached to frame 100. In the simplified device of FIG. 1, no edge sensor is used. Instead, it is assumed that individual tracks are spaced apart sufficiently to permit individual track addressing by merely placing the angular position of guide bar assemblies 121a and 121b at preset orientations. i

In both FIGS. 1 and 2, data is transmitted to and received from heads 111 via slip rings 117. These may be mechanical, employing brushes, or operate inductively. The stationary elementof the slip rings may be connected via a conductor (not shown) to a central computer or other data processing device. The moving element of each slip ring 117 may be connected to a single head Ill. Alternatively, switching circuitry may be included within drum 101 to multiplex several heads 111 into one slip ring 117.

In operation, power supplied to motor 103 causes drum 101 to spin at a speed causing the exterior surface of the drum to have a circumferential speed around 2,500 in/sec. This speed permits short access time and high data rate and also creates a natural foil or air bearing clearance between strip 102e and drum 101. Alternatively, the curved surface of drum 101 may be provided with holes through which air is forced. thereby creating an air bearing interface if lower speeds are used. The guide and idler bars may be mounted to rotate aboutthelr longitudinal axes. Preferably, however, they are non-rotating, and have holes 703 (FIGS. 74 and 7b) placed 5 interior to the lines. of tangency of strip 102 on the surface encircled by strip 102. Compressed air is forced through these holes, thereby creating the air bearing interface between strip 102 and the surfaces with respect to which it may slide.

To describe operation of the invention as clearly as possible, the simple embodiment of FIG. 1 will first be explained. A track on strip 102 can be specified in terms of the angular position of the assemblies 121a and 1211). Referring to FIG. 4 briefly, the angular position for guide bar assembly 121b will be measured in the horizontal plane containing the axis of the convex cylindrical surface of bar 106b clockwise from the vertical plane to this axis. This angle will be referred to as angle B. For assembly 121a, the equivalent angle will be referred to as angle A, and measured in the horizontal plane counterclockwise from the vertical plane to the axis of the convex surface of bar 106a.

Strip segment 102e may be placed at any position along the entire length of drum 101 properly setting angles A and B. However oriented, it is important that these angles be equal. In the position shown in FIG. 1, these angles are near a minimum and segment 102e is nearly as far to the right on drum 101 as possible. If strip 101 is bilaterally symmetrical, or uniform, in cross section and has uniform modulus of elasticity a single equilibrium position of segment 102e exists for any specific angle assumed by assemblies 121a and 121b. If strip segment 102e is not at the equilibrium position for the values of angles A and B, unequal tension in strip 102 exists caused by differences in the path length across the width of strip 102. This creates lateral forces which tend to shift segment 102e to the equilibrium position. To permit segment 102e to accurately reach its equilibrium point, it is necessary that the contact of strip 102 with the bars on which it slides be almost frictionless. The lateral forces present when strip segment 102e nears its equilibrium point are quite small, and even slight friction will cause inaccuracies. The use of air bearings between strip 102 and all surfaces on which it slides reduces friction to a very satisfactory level.

With the assemblies 121a and 121b in the position shown in FIG. 1, with each rotation of drum 101, head 111 passes adjacent a thin, longitudinal part of strip segment 102e which forms the track on which data transducing occurs. To address a different track, angles A and B are changed. Voice coils 114a and 114b are simultaneously energized to move armatures 115a and 1151; respectively to new positions causing new, equal A and B angles to be formed. For illustrative purposes, assume that armatures 114a and 114k in FIG. 1 are both retracted equal, slight amounts, i.e., angles A and B both increase slightly. The position of strip segment 1022 is no longer at equilibrium position. As the new equilibrium position is approached, the lateral forces created by the unequal tension across the width of strip 102 decrease. When these forces equal the opposing frictional forces, lateral movement of strip 102 ceases and the new track accessed by head 111 is ready for data transcribing.

To analytically relate the lateral displacement of strip 102 to the physical parameters controlling this displacement, reference can be had to FIGS. and 9b. Shown therein is a part of guide bars 10512 and 106b over which an edge of strip 102 is shown wrapped. For' ease in analysis, bars 106b and b are shown as cylindrical and having equal diameters. FIG. 9a shows aprojected view of these three elements in a plane parallel to the horizontal plane of assembly 121b, and FIG. 9b

shows a side projected view of the same perpendicular to the axes of guide bars 105b and 10Gb. The parameters of which the displacement or offset A is a function are: guide bar angle or, diameter D of guide bars lb and Gb; and relative location of the centers of bars 105b and l06b shown in terms of dimensionsf and a. a is a signed distance measured from the center of bar 105!) on FIG. 9b, positive upwards. Thus, if the center of bar l06b were above the center of bar 105b (and thus only a relatively small surface of each bar was encircled by strip 102), a would be positive, i.e., measured upward. In FIG. 9b, a is negative. In the actual formula, a second dimension is used for purposes of simplifying the expression.

l= V a +f D and arc cos [(al +fd)/(a +f")] is in radians and is in the third quadrant whenf D (as in FIG. 9b) and in the second quadrant whenf D and the argument is negative. The expression are cos [al +fd/a +f is the wrap angle, i.e., the total are subtended by the radii connecting the tangent lines of strip 102 with the center of bar 1051) or 106b. This formula is based on the assumption that the tension across the width of strip 102 is uniform and that unequal tensions in strip 102 caused by moving guide bar assemblies 121a and l21bare equalized by the equilibrium position of strip 102 reached in each case.

The devices of FIGS. I and 2 vary a to change A to the desired value. A is seen to be a function of sin a only, once a geometrical configuration has been chosen. a is easily written in terms of the amount armatures 115a and 115b are extended, and A can then be expressed as a function of armature position only. The positions for a number of tracks over the width of strip l02e are selected, the amount of offset required for each can be easily determined, and the formulae solved for the armature position required for addressing each track. The external controller (205 in FIG. 2) supplying strip shifting or voice-coil signals on lines 1190 and ll9b can be easily programmed to supply the desired one, of a discrete set of signals which. positions armatures 114a and 11411 to allow addressing the desired track.

In FIG. 2, a complete, operational system is displayed. The means employed in shifting stripsection 102e are exactly the same as in FIG. 1. However, for high speed data processing, the apparatus of FIG. 1 does not store a sufficient amount of data to be competitive with alternative storage means. Since the two systems are similar, FIG. 2 will be described in terms of the differences between the apparatus it displays and that of FIG. I.

The apparatus of FIG. 2 is almost identical to a prototype device now in operation, differing only in that guide bar assembly pivots 122a and l22b (see FIG. 1) are positioned midway between the ends of assemblies 121a and l2lb. This change was made for ease in displaying and explaining the operation of the invention by not obscuring the assemblies. FIG. 8 displays the preferred arrangement.

Drum 101 of FIG. 2 has been changed inthat, as previously explained, a plurality of heads 111 are present, the pair of dotted lines indicating their position on drum 101. Addition of several heads to drum 101 permits more rapid accessing of a desired track because strip section 102 need not be moved as great a distance, on the average, in each accessing operation.

Strip 102 in the device of FIG. 2 is long enough to have many blocks of data on it, a block being the designation for all the data that may be accessed by heads 111 by only moving strip segment 102s laterally. The excess length of the strip 102 is stored on spools or capstans 208a and 208!). Driving reels 208a and 208!) are reel drive motors 210a and 2l0b respectively (see FIG. 4). Strip segment 102a, immediately adjacent strip roll 20lb on reel 208b, extends to, and partially encircles idler bar 202b. Idler bar 202b is necessary in this embodiment to preserve the parallel relationship between strip segments l02b and 102d. Without idler bar 202b present, as the diameter of strip roll 20lb varied with varying amounts of strip 102 stored on spool 208b, the required condition of parallelism could notbe maintained. Idler bar 202a is added adjacent strip roll 201a for the identical reason. Strip edge sensors 212a and 2l2b are attached to frame 100 and placed adjacent the edges of strip segments 202i and 102a, respectively. Sensors 212a and 212b detect the position of the edge of the adjacent strip segments; and transmit signals encoding the lateral position of strip segments 102i and 102a via data lines 238a and 238b respectively, to controller 205.

The fact that the strip ends are held by spools 208a and 208b, rather than by clamps necessitates control means to maintain proper strip tension. Responsive to strip control unit 302 (FIG. 3), drive motors 210a and 21% cooperate to keep proper tension on strip 102. By providing for opposing torques from drive motors 210a and 21% creating equal and opposing forces at the unrolled strip section adjacent rolls 201a and 201b, the proper tension on strip 102 is maintained. Although a wide range of tension may be suitable for a given strip 102, with a strip comprising a 0.0015 in. MYLAR (registered DuPont trademark) plastic film base 22 in. wide, tension ranging from 50 to lbs. has been found satisfactory.

Controller 205, in addition to providing all the various control functions necessary in operating the apparatus, also receives commands and status information from an external data processor 225, for which this invention forms a piece of peripheral equipment. The controller per se, does not constitute any part of this invention. Design ofa controller providing the proper control signals to the apparatus and correctly interpret the command status signals received by it, is a matter of design techniques well known in the art. Therefore, controller 205 will be discussed only in terms of the block diagram of FIG. 3, in conjunction with the overall discussion of the operation of this embodiment.

The embodiment of FIG. 2 has greater capacity than that of FIG. 1 not only because of the greatly enlarged area available for data storage, but also because of increased density at which data is stored. One of the significant advantages of the invention lies in the fact that very accurate lateral positioning of strip segment 102e is possible if feedback techniques are used. A strip position sensor is therefore provided. The strip position sensor comprises voice coil 21% attached to frame with armature 2l8b projecting toward strip segment l02e and generally parallel to the axis of drum 101. Attached to the end of armature 218b adjacent strip 102e is sensing element 220b. Sensing element 220b senses the position of strip segment 102a relative to it and transmits data encoding this position in the form of a sensing element position signal to controller 205 via data line 221b. The position of armature 2l8b is sensed by sensing element position sensor 217b which is attached near voice coil 21% in such a manner that the distance armature 218b is extended can be sensed and the position encoded and transmitted via data line 227b to controller 205. A similar means for detecting the position of the right-hand portion of strip segment 102e is shown in FIG. 4 as comprising voice coil 219a with armature 218a, strip position sensor 220a, sensing element position sensor 217a and data lines 221a, 236a and 227a.

Continuing to describe FIG. 2 in terms of differences from FIG. 1, several more variations are necessary to realize the improved operation of which the embodiment of FIG. 2 is capable. Since a plurality of heads 111 are employed, it is unnecessary to shift strip segment 102e laterally a distance greater than the greatest distance between a pair of adjacent heads 111 to permit access to every track on strip segment 1022. Thus, the variation in angles A and B is also greatly reduced, as is the maximum movement of armatures 115a and ll5b. Not only is track addressing thereby speeded up by the use of multiple heads, but data rates may also be increased, since it is a simple matter to arrange for all or several of the heads 111 to simultaneously transcribe data.

In a preferred design, 16 heads, each separated from those adjacent by 1.3 inch, are aligned on the surface of drum 101 as indicated by reference numeral 111 in FIG. 2. Track density, i.e., the distance between the centers of adjacent tracks, is 0.01 inch in a preferred design. Thus, I30 tracks are accessed by a single transducing head 111. The location of each track on strip segment l02e can be specified in terms of a fixed distance from the left edge of strip segment 102e. Sensing elements 220a (see FIG. 4) and 220b in conjunction with sensing element position sensors 217a and 2171; precisely measure the distance of the left edge of strip segment 102:: from a vertical datum plane when sensing elements 220a and 220b are at a preferred position with respect to an edge of strip segment l02e. This vertical datum plane, fixed with respect to heads 111, is perpendicular to the axis of drum 101- and passes through the sensing element position sensors 217a and 2I7b. Thus, the known distance of a desired track from the left edge of strip segment l02e plus the measured distance of this edge from the datum plane (i.e., armature length) must equal the known, fixed distance ofa magnetic head 11] from the datum plane, in order for the desired track to be accessed by a head. If the two quantities are not equal, angles A and B are adjusted by signals from controller 205 to voice coils 114a and 1141; to cause strip segment l02e to move laterally and equalize these two measurements. If track to edge distance plus measured armature length (edge to datum plane) is less than the known head to datum plane distance, angles A and B must be descreased to cause strip segment 102e to shift to the right, increasing the measured distance of the left edge of strip 102e from the datum plane. If the sum of track distance and edge distance is greater than head distance, angles A and B must be increased. Similarly, if the opposite ends of segments'102e are at unequal distances from the vertical datum plane, controller 205 adjusts the angle of the appropriate guide bar assembly by changing the position of the armature of voice coil 114a or 11411 only.

FIG. 3 discloses the elements of controller 205 and a preferred embodiment of the strip edge sensor assembly. Block numbers of the strip are transmitted to control unit 302 from an external source, such as data processor 225 (FIG. 2), via line 230b. Track and head numbers are transmitted to address decoder 301 via line 230a from the external source. The track address is transmitted from address decoder 301 to sensor position control 302 via line 304. In the preferred embodiment of the strip edge position sensor, armature 2l8b still carries sensing element 220b. But bracket 222b has been changed to enable it to carry a second sensing element 228b on the opposite side of strip 102. The sensing element signals are transmitted on lines 2161: (for sensor 228b) and 22111 to strip control unit 302.

The distance separating the sensitive areas of sensing elements 220b and 228b is approximately equal to the width of strip 102 so as to allow the outputs of the sensing elements to simultaneously vary with relative motion between bracket 222b and strip segment 102a. At one relative position of bracket 222 with respect to segment 102e, the balance position, the output of elements 220b and 228b are equal. Normally, this will be when segment 102e is located symmetrically between them, covering an equal part of the sensing area of each. Sensor 217b detects movement of scale 2l5b-and transmits sensing element position signals via line 227b to sensor position control 303. Strip control unit 302 receives signals from block sensor 211 mounted adjacent sensor 220b (see also FIG. 2) via line 237, and from the left and right rewind sensors 212b and 212a respectively via lines 238b and 238a. Strip control unit 302 supplies control signals to voice coils 114a and l14b via lines 119 a and 119b, respectively, and to the left and right reel motors 2101) and 210a, via lines 232b and 232a respectively. Sensor position control 303 supplies sensor shifting signals to voice coil 21% via line 236b.

Similar structure exists for sensing the position of the part of segment l02e adjacent idler bar a. Extra identical, signal lines (not shown) convey the signals generated there-from to strip control unit 302 and sensor position control 303. It was found necessary to sense strip position at both ends of segment l02e in order to prevent skewing the strip segment with respect to the path of head 111.

Control of track selection is one of the functions of controller 205. To expedite this selection, in the preferred embodiment 16 heads present on drum 101 (FIG. 2) may be numbered left to right, 0 through 15. Each head is used to accessthe already-mentioned group of I30 side-by-side tracks. Thus, the tracks accessed by head 0 are the leftmost I30, those referenced by head 1 are the lying closest to those accessed by head 0, etc. Each individual track in a contiguous group of I30 accessed by a single head 111, may be given an identifying number 0 through 129 from left to right as shown in FIG. 3. Thus, in a given block, each track may be uniquely identified on the basis of its head and track numbers. Each track address received from data processor 225 on data line 230a contains this information. Address decoder 301 computes the distance the left edge of strip segment 3102b must be from the vertical datum plane to permit the specified head 111 to reference the desired track. This is done by forming the product of the track number and 0.01 inch, and summing this product with the known distance of track of head 0 from the left edge of strip segment 102a. As previously explained, the sum of this distance plus the distance of the left edge of strip segment l02e from the datum plane as measured by sensors 21712 and 217a must equal the fixed distance that head 0 is from the datum plane to permit addressing the desired track.

In the strip position sensors shown in FIG. 3, the sensing elements are photocells. Accordingly, it is necessary to have light sources supplying light to them. Referring to the magnified view in FIG. 3, light source 229b is located on bracket 222b so that its output is directed across the right-hand channel in bracket 22212 and onto the sensing area of photocell 228b. A similar arrangement is present for photocell 220k. As bracket 222b and strip segment 102e shift relative to each other, none, part, or all of the light directed toward a photocell will strike the sensitive area, thereby varying the sensing element signal being sent from the photocell to strip control unit 302. Photocells are but one kind of sensing element which will provide the accuracy needed. A pair of air jets located in the positions occupied by the photocells are an acceptable alternative. As strip segment l02einterrupts, partly or completely, the flow of air from each orifice, upstream pressure and flow rate will vary, furnishing a physical quantity which may be measured to determine relative strip segment l02e position. Mechanical fingers or feelers driving a potentiometer are another possibility.

Voice coil 21%, armature 218b, edge sensors 228b and 220b, and sensor control 303 comprise a servo system. Strip control unit 302 endeavors to maintain strip 102 in the balance position with respect to photocells 228b and 220b at all times. Normally, sensor control unit 303 keeps a sensor shifting signal on line 236b to voice coil 2l9b keeping the position of armature 218k fixed. If strip 102 shifts to the right relative to photocells 220!) and 228b (perhaps caused by a slight error in the strip shifting signal received by voice coil ll4b), photocell 22% will become more uncovered and photocell 228b will become less covered. Signals from these photocells reaching strip control unit 302 will become unbalanced, that from photocell 22% being relatively greater than that from photocell 228b. Strip control unit 302 detects this difference and varies the strip shifting signal to voice coil 21% to shift strip segment 102e further to the left, tending to cause sensor 220b to be more covered, and sensor 228b to be less covered. As strip segment 102s approaches the balance point, the difference between the two signals from sensor 228b and 220b decreases, and when perfectly balanced, voice coil 114k ceases movement of armature 2l8b except for possible slight hunting inherent in the servo loop. Thus, sensors 220b and 228b can be considered to provide signals to control unit 302 exactly specifying the movement of strip segment 102e necessary for precise addressing of the desired track. A similar assembly controls the position of the end of strip segment 102a adjacent idler bar 110a.

When it becomes necessary to address a different track, a second servo loop is energized. As explained previously, the output of the address decoder on line 305 to sensor position control 303 specifies the position which armature 21% should assume to place strip segment 102e in position to permit addressing of the specified track when strip segment l02e is in its balance position with respect to bracket 222b. This signal is the set point. When the track specified to address decoder 301 changes, sensor position control 303 changes the sensing element position signal to voice coil 21% to start driving bracket 22212 to the desired position. The movement of armature 2l8b destroys the balance position. Strip control unit 302 detects the lack of balance between the output of sensing elements 220b and 228b (the feedback, or error, signal) and immediately reacts as explained above, to restore the balance position. Ideally, the response by strip control unit 302 and voice coils 114a and 1114b is so rapid, that strip 102 will follow along bracket 222k without getting more thana few hundredths of an inch away from the balance position. When armature 2l8b reaches the position which will place the end of strip segment 102a in proper position when strip segments 21% reaches the balance position, this'fact will be detected by sensor position control 303 from the sensing element position signal on line 227b. The sensor shifting signal is then changed to halt movement of armature 218 b.

A similar arrangement positions the end of strip segment 102e adjacent idler bar a. Both the feedback and set point signals maybe digitized in which case a digital comparison is performed. To d'esensitize servo operation somewhat, a preselected difference between them may be designed into the controls which must be exceeded before either strip or sensor position is corrected. Mechanisms such as this have been employed for many years in, e.g., disc memories for track selection. Thus no great difficulty is presented to a skilled designer in adapting such controllers to the present device.

Referring next to FIG. 10, therein is shown an alternate embodiment of the controller. The apparatus of FIG. 3 causes strip 102 to follow the strip position sensors as it moves responsive to a change in the track specified. It is also possible to move strip segment 102e responsive to the track address signal, and follow the moving strip with sensors 220a and 220b, relying on the sensing element position signal to indicate when the specified track is in position for addressing. In this situation, it is necessary that strip segment 102a move slowly enough to permit voice coils 119a and 11% to keep up3[ with it. Accordingly, in H0. 10 is shown a strip control unit 302 receiving the track address signal online 304, and supplying strip shifting signals on lines 119a and 11% to voice coils 114a and 1114b. These signals cause strip segment 102a to shift toward the desired position. As strip segment 102e moves toward its new position, sensing elements 22% and 228b will lose their balance position and change the sensing element signal on 22lb and 2l6b. Sensor position control 303 reacts by transmitting a sensor shifting signal on line 236b to voice coil 21% to cause armature 21812 to move bracket 222b back into the balance position. This movement is detected by sensing element position sensor 217b and transmitted to strip control unit 302 on line 227b. This signal closes the loop. If the sensing element position signal on line 227b is an accurate measure of the actual position of strip segment 102e, then by merely comparing it to the track address signal, the movement of strip segment 102e can be stopped at the position allowing addressing of the specified track.

Referring again to FIG. 2, the operation of moving a new data block into position for access by heads 111 will be explained. For convenience each block on strip 102 may be assigned a number, the numbers starting with l for the innermost block on spool 208b, and increasing consecutively toward the innermost block on spool 208a. When a new block number is received by control unit 302, it must compare this number with the number of the block currently in addressable position. Accordingly, there is provided within controller 205 means for storing the current block number of the currently addressable block. By comparison of the relative magnitudes of the two values, the direction and the number of blocks to travel to reach the new block may be easily determined. Control unit 302 issues signals to left and right reel motors 21% and 210a causing these reel motors to simultaneously pay out the correct length of strip from the correct reel and take up a similar length of strip on the opposite reel.

It is very important that strip rolls 201a and 20lb be accurately rolled up, i.e., that the edges of successive.

layers of strip 102 be precisely on top of one another so that the strip will be accurately positioned to permit accurate positioning of segment 102e. Therefore, when a portion of strip 102 is to be wound on one roll and unwound from the other, both guide bar assembly angles A and B may be positioned so no offset at all exists in the position of strip segment l02e. When a larger numbered block is desired, a portion of strip 102 will be unwound from roll 201a and wound onto roll 20lb. Strip edge sensor 212b continuously monitors the position of strip segment 102a and signals the occurrence of any detectable deviation from the preselected position to control unit 302 via line 238b. Control unit 302 reacts by causing voice coil 114!) to change angle B very slightly as needed to correct this deviation.

A marker must be present between each block of data on strip 102 for detection by interblock marking sensor 211. As each marker passes beneath sensor 211, a signal transmitted to control unit 302 permits the updating of the current block number register. Sensor 211 may conveniently bea photocell and have an adjacent light source shining onto strip 102. In such a case, each interblock marking may be a small, silvered piece of tape attached adhesively to strip 102 so as to pass beneath sensor 211 as the strip is unwound from one reel and wound up on the other and reflect light from the source to the photocell. Alternatively, the interblock markers may encode the actual block number of the adjacent block, thereby permitting direct detection of each block number.

Referring next to FIG. 5, therein is shown an alternative strip-shifting means. The geometrical relationship of guide bars l05b and 106b and 105a and 106a, with respect to each other and strip 102 must be the same as for the device of FIG. 1. Guide bars 105b and 105a slide in slots 501k and 501a respectively. The position of guide bar 105k is controlled by voice coil 114k and armature 1l5b supported by bracket 503b. The force from armature 1l5b to move bar 10511 in slots 501b is exerted through bracket 502b. (Only the slots 501a are shown for bar 105a, but the construction for the elements not shown is identical.

In operation, the apparatus of FIG. 5 depends for the shifting of strip 102 on a fixed slight angle which each pair of guide bars make with the vertical plane. Arbitrarily, these angles have both been chosen as obtuse,

when measured as angles A and B in FIG. 4 are measured. The path of movement of guide bar b in slots 5011) is parallel to strip segment 1021;. Similarly, the movement of guide bar 105a in slots 501a must be parallel to the plane in which strip segment 102f lies.

In FIG. 5, the distance between guide bars 10512 and 106b is near its maximum. According to formula 1, offset can be controlled by varying dimension a. Since an gles A and B are both obtuse, the strip is offset to the left near its maximum amount when guide bars 105a and 1051; are in the positions displayed. As dimension a is decreased for each pair of guide bars, offset decreases and strip segment 102e shifts to the right. Thus, by simply positioning guide bars 105a and l05b properly, strip segment 102e may be shifted axially on drum 101. Depending on the distance which segment 102e must be shifted, the obtuseness of angles A and B, and the change possible in dimension a may have a wide range of variation.

When moving strip 102 for accessing a new block, the position of the movable guide bar adjacent the takeup spool can be slid back and forth in its slots to precisely steer strip 102 onto the takeup spool. The remainder of the operation is identical in concept to that of the device of FIG. 2.

FIGS. 7a and 7b detail the means for creating the air bearing interface between strip 102 and those surfaces over which it slides axially. Guide bar l05b has been arbitrarily selected for purposes of illustration. Line 701 forms the center lines of orifices 703 placed on the surface of guide cylinder 1051:. Line 702 is the tangent line which strip segment 102d forms with cylinder l05b. For most effective creation of the air bearing interface, the arc subtended by lines 701 and 702 should be 5. It should of course be understood that two sets of orifices 703 are necessary, adjacent each tangent line formed by strip 102 with the bar. In a preferred design, orifices 703 are each 0.03 inches in diameter and are spaced at 0.8 inch intervals. An external compressed air source provides a pressure of 8 psig at each orifice.

FIG. 8 displays the previously mentioned alternative embodiment for pivoting a pair of guide bars. A pair of voice coils 806 and 808 are provided at opposite ends of guide bar assembly l2lb. Pivot 805 is located central to the ends of the guide bars. Voice coils 806 and 808 are arranged to assist each other in pivoting guide bar assembly 121a. That is, when the armature of one extends to pivot guide bar assembly 121b, the armature of the other is being simultaneously retracted by the signals from controller 205. Several advantages accrue from this arrangement. The guide bars may be moved to a new angle more rapidly in this configuration, because the rotational inertia of the guide bar assembly about the pivot is decreased with a central pivot. Vibration of the guide bar assembly is decreased as well, because the guide bar assemblies are supported at three rather than two places.

It should be clearly understood that the embodiment, and variations thereon, described above exemplify but a few of the many forms which this invention may take.

Not wanting to be limited by this description, but only by the following, what I claim is:

1. apparatus for accessing with a data transducer having a transcribing surface, a longitudinal recording track on an elongate flexible recording strip and specified by a track address signal, comprising:

a. a frame;

b. first and second strip holders attached to the frame at spaced apart locations and holding the strip at, respectively, first and second areas on the strip between which is located a first strip section having at least two recording tracks on its surface;

c. transducer holding means for maintaining the transcribing surface of the data transducer within a predetermined data transcribing distance of the first strip section and moving the transducer relative to the first strip section in a path having a shape substantially the same as the recording tracks;

d. means for shifting only the first strip segment,

transversely to the recording tracks on it, to a position with respect to the transducer specified by a strip shifting signal; and

e. control means receiving the track address signal, for determining the strip position placing the track specified by the track address signal within the predetermined data transcribing distance of the transcribing surface of the transducer, and supplying a strip shifting signal to the strip shifting means spcifying this position.

2. The apparatus of claim 1 wherein the strip shifting means comprises:

a. first through fourth guide bars at least a part of the exterior of each being a convexly curved cylindrical surface;

b. a first adjustable guide bar support attached to the frame in a position holding the first and second guide bars againstopposite strip surfaces between the transducer and the first holder with the convex surface of these two bars at least partially encircled by the strip, and forming the strip into second, third, and fourth flat sections tangent to the convex surface of the first, second, and both guide bars respectively, with the tangent lines of the fourth sec tion with the first and second convex guide bar surfaces being parallel;

c. a second adjustable guide bar support attached to the frame in a position holding the third and fourth guide bars against opposite strip surfaces between the transducer and the second holder with the convex surface of each bar at least partially encircled by the strip, and forming the strip, into fifth, sixth and seventh flat sections tangent to the convex surfaces of the third, fourth and both guide bars respectively with the tangent lines of the seventh section with the third and fourth convex guide bar surfaces being parallel; and

d. first and second means moving the first and second guide bar supports respectively and changing the positions of the guide bars relative to the transducer holding means for shifting the strip transversely with respect to the recording tracks thereon to the position specified by the strip position signal.

3. The apparatus of claim 2 wherein the first and second guide bar supports include respectively first and second pivots attached to the frame and positioning the bars to make the second and fifth strip sections parallel respectively to the fourth and seventh strip sections and perpendicular respectively to the axes of rotation of the first and second pivots; and wherein the support moving means includes means for pivoting the first and second guide bar supports about their respective pivots.

4. The apparatus of claim 3 wherein the guide bar support pivoting means further comprises means for pivoting the first and second guide bar supports substantially equal amounts.

5. The apparatus of claim 3 wherein each support pivoting means further comprises a voice coil connected between the support and the frame.

6. The apparatus of claim 3 wherein the first and second guide bar supports further comprise respectively first and second pivots attaching their respective supports to the frame at points between the ends of the bars held by each support, and wherein each support pivoting means comprises a pair of elements each having a pair of spaced apart control points whose distance apart varies responsive to the strip position signal, a control point of one element attached to its associated support with the other control point of each element attached to the frame.

7. The apparatus of claim 6 wherein each element comprises a voice coil having one control point on the armature and the other on the field.

8. The apparatus of claim 7 wherein the lever arms formed between each support pivot and the points of attachment of the element control points to it are equal; and wherein each pair of elements comprising a support pivoting means comprises positioning devices whose distance between control points varies equally responsive to identical strip position signals.

9. The apparatus of claim 8 wherein each positioning device comprises a voice coil attached so as to substantially form a right angle with a line connecting the points of attachment of the voice coils to the support when the strip is approximately midway between its extreme positions.

10. The apparatus of claim 6 wherein increase in the distance between the control points of each element comprising a support pivoting means urges the support to rotate in thesame direction.

11. The apparatus of claim 2 wherein the first and second guide support moving means each include respectively means for causing the distance between the first and second and the third and fourth bars to change maintaining meanwhile the specified geometric relationships, and further comprising means for attaching the guide bar supports to the frame in a position placing the lines of tangency formed by the fourth, and seventh strip sections at predetermined angles to a plane perpendicular to the drum axis, and placing the second and fifth strip sections parallel respectively to the third and sixth strip sections.

12. The apparatus of claim 11 wherein the bar distance changing means further comprises means for maintaining the distances between the first and third, and second and fourth, guide bar substantially equal.

13. The apparatus of claim 11 wherein the support attaching means further comprises means for attaching the guide bar supports so as to place the bars at substantially equal angles to the data track.

14. The apparatus of claim 1 wherein the transducer holding means comprises a circular drum rotatably mounted on the frame and partially encircled by the first strip section, and having the transcribing surface of the data transducer embedded in and facing outwardly from its curved surface.

15. The apparatus of claim 14 further comprising a. first and second idler bars, at least a part of the exterior of each being a convexly curved cylindrical surface;

b. a first idler bar support attaching the first idler bar to the frame immediately adjacent the drum with the convex surface of the first idler bar at least partially encircled by the strip and the lines of tangency formed by the strip section between the first idler bar and the drum substantially parallel; and

c. a second idler bar support attaching the second idler bar to the frame immediately adjacent the drum on the side opposite that of the first idler bar with the convex surface of the second idler bar at least partially encircled by the strip and the lines of tangency formed by the strip section between the first idler bar and the drum substantially parallel.

16. The apparatus of claim 14 including means for maintaining an air bearing interface between the strip and at least one surface with respect to which it slides.

17. The apparatus of claim 16 wherein the air bearing means comprises a plurality of areas on the surface upon which the strip slides, each containing at least one aperture, and means for forcing air through the apertures.

18. The apparatus of claim 17 wherein the aperture is located in the cylindrical surface approximately degrees from a tangent line of the strip section and between the tangent lines.

19. The apparatus of claim 1 wherein the strip holders include means for applying tension within a predetermined range between them to the first strip segment.

20. The apparatus of claim 1 wherein the strip holders each further comprise means for maintaining equal tension across the width of the strip and total tension within a predetermined range in the strip.

21. The apparatus of claim 20 wherein the equal tensioning means further comprises first and second clamps, each non-slippingly gripping one end of the strip across substantially its entire width and attached respectively to the first and second strip holders.

22. The apparatus of claim 1 wherein the first and second strip holders comprise, respectively, first and second storage spools rotatably attached to the frame; and means receiving the track address signal, for rotating each spool to unwind a length of the strip from one spool and concurrently take up a similar length on the other spool, responsive to the track address signal.

23. The apparatus of claim 22 wherein the storage spool rotating means further comprises means applying opposing torque to the spools for maintaining strip tension within predetermined limits.

24. The apparatus of claim 22 further comprising third and fourth idler bars, at least a part of the surface of each having a convexly cylindrical shape and both attached to the frame, the cylindrical surface of the third always at least partially encircled by the strip portion immediately adjacent the second takeup spool, the tangent lines of each strip section between each idler bar and its associated storage spool being parallel and coplanar.

25. The apparatus of claim 22 further comprising third and fourth idler bars, each having a partially convex cylindrical surface and each attached to the frame to allow the strip segments immediately adjacent the first and second storage spools to at least partially encircle the convex surfaces of the first and second idler bars respectively.

26. The apparatus of claim 22 wherein the strip has a plurality of block markers at predetermined intervals, and wherein the track address signal includes a block address signal; wherein the spool rotating means further comprises means receiving a block location signal for taking up on one spool and unwinding on the other spool, a sufficient length of strip to position an addressed block to partially encircle the drum;

and wherein the control means further comprises means sensing the current position of the strip for supplying a block location signal to the spool rotating means.

27. The apparatus of claim 26 wherein the strip includes a plurality of unique block markers longitudinally spaced, and wherein the strip position sensing means includes a sensor identifying each marker as the strip is moved.

28. The apparatus of claim 1 wherein the control means comprises:

a. a strip position sensor, including a strip sensing element, attached to the frame, and supplying a strip position signal specifying the strip position; and

b. a controller receiving the strip position signal and the track address signal, comparing them to determine the strip shifting signal to move the strip to the position for addressing the specified track, and supplying this strip shifting signal to the strip shifting means.

29. The apparatus of claim 28 wherein the strip position sensor comprises a strip edge sensor.

30. The apparatus of claim 28 wherein the strip position sensor comprises a strip edge sensor issuing a strip position signal specifying the position of the edge of the first strip segment.

31. The apparatus of claim 28 wherein the strip position sensor includes a carrier movably attaching the sensing element to the frame and shifting the element in a path substantially parallel to the axis of the drum responsive to a sensor shifting signal, and supplying a signal specifying the position of the sensing element.

32. The apparatus of claim 31 wherein the controller further comprises means for shifting the sensing element responsive to the track address signal to a position causing the strip position signal to have a predetermined value when the specified track is being addressed, and for supplying a strip shifting signal to the strip shifting means causing the strip to shift until the predetermined strip position signal value is reached.

33. The apparatus of claim 31 wherein the strip position sensor comprises a pair of strip edge sensors each furnishing a strip position signal varying as the strip moves between a pair of predetermined positions relative to the edge sensors.

34. The apparatus of claim 33 wherein each edge sensor comprises a photocell.

35. The apparatus of claim 31 wherein the controller further comprises:

a. means supplying a strip shifting signal to the strip shifting means responsive to the track address signal, for causing the strip to move laterally toward the position permitting addressing of the specified track by the head and to stop the lateral strip movement responsive to an accessing value of the sensor c. wherein the strip position sensor includes means for supplying the accessing value of the sensor posi tion signal to the controller when the strip approaches the specified position.

36. The apparatus of claim 1 wherein the transducer holding means comprises a circular drum rotatably mounted on the frame and positioned to be partially encircled by the first strip section, and having the transcribing surface of the data transducer embedded in and facing outwardly from its curved surface, and wherein the strip shifting means comprises:

a. first through fourth guide bars at least a part of the exterior of each being a convexly curved cylindrical surface;

b. a first guide bar support movably attached to the frame and positioned to hold the first and second guide bars against opposite strip surfaces between the transducer and the first holder with the convex surface of each bar at least partially encircled by the strip, and forming the strip into second, third, and fourth flat sections tangent to the convex surfaces of the first, second, and both guide bars, respectively, with the tangent lines of the fourth section with the first and second guide bar convex surfaces being parallel;

c. a second guide bar support movably attached to the frame and positioned to hold the third and fourth guide bars against opposite strip surfaces between the transducer and the second holder with the convex surface of each bar at least partially encircled by the strip, and forming the strip into fifth, sixth and seventh flat sections tangent to the convex surfaces of the third, fourth and both guide bars, respectively with the tangent lines of the seventh section with the third and fourth guide bar convex surfaces being parallel; and

d. first and second means moving the first and second guide bar supports respectively and changing the positions of the guide bars relative to the transducer holding means for shifting the strip transversely with respect to the recording tracks thereon to the position specified by the strip position signal.

37. The apparatus of claim 36 wherein the first and second guide bar supports include respectively-first and second support pivots attached to the frame and positioning the bars to make the second and fifth strip section parallel respectively to the third and sixth strip sections and perpendicular respectively to the axes of rotation of the first and second pivots; and wherein the support moving means includes means for pivoting the first and second guide bar supports to cause the first strip section to shift responsive to the strip position signal to a position relative to the transducer permitting the addressed track to be traversed by the transducer as it moves relative to the first strip section.

38. The apparatus of claim 37 wherein the support pivoting means further comprises means for maintaining the axes of the bars supported by the first support at an angle measured clockwise from the axes to a plane perpendicular to the drum axes, equal to the angle measured counterclockwise from the axes of the bars supported by the second support, to the plane.

39. The apparatus of claim 37 wherein the first and second strip holders comprise respectively, first and second storage spools rotatably attached to the frame and means receiving the track address signal, for rotating each spool to unwind a predetermined length of the strip from one spool and concurrently take up a similar length on the other spool, responsive to the track address signal; and to maintain a predetermined tension in the strip section between the taken-up lengths on the spools during transducing operations.

40. The apparatus of claim 37 including a strip position sensor mounted on the frame and supplying a signal specifying the location of the first strip segment relative to the data transducer path to the strip position control means; and wherein the strip position control means further comprises a comparator receiving the track address signal and determining therefrom the transverse position of the strip permitting the data transducer to access the track, comparing the strip location to the strip location permitting track access, and issuing the strip position signal to the strip shifting means.

41. The apparatus of claim 40 wherein the strip position sensor comprises a strip edge sensor issuing a strip edge position signal specifying the position of the edge of the first section relative to the data transducer path.

42. The apparatus of claim 36 wherein at least one guide bar includes means for creating an air bearing contact between the strip portion encircling it and the guide bar.

43. The apparatus of claim 42 wherein the air bearing creating means comprises a plurality of areas on the strip-encircled surface of the guide bar having orifices therein, and means for supplying compressed air to these orifices.

44. The. apparatus of claim 43 wherein at least one orifice is set approximately 5 from a tangent line of the strip with the guide bar and between the two tangent lines.

45. The apparatus of claim 1 wherein the strip shifting means comprise:

a. first and second guide bars and third and fourth guide bars, comprising first and second guide bar pairs respectively, at least a portion of each guide bar being a convexly curved cylindrical surface; a

b. a first guide bar mount supporting the first pair of guide bars, and a second guide bar mount supporting the second pair of guide bars, the guide bars comprising each pair being in spaced apart and substantially parallel relationship to each other, each mount being attached to the frame in a position such that: when the strip is held by the holders, is passed between the first and second, and the third and fourth guide bars, is partially wrapped around the convex surface of each guide bar, and is drawn taut, the flat strip surfaces adjacent and external to the first pair of guide bars are substantially parallel, the flat strip surfaces adjacent and external to second pair of guide bars are substantially parallel, and the guide bars are angled to the longitudinal axis of the strip causing an offset of the strip between the two pairs of guide bars to change the offset of the strip between the two pairs of guide'bars; and

c. means receiving the strip shifting signal for varying the positions of the guide bars to change the offset of the strip between the pairs of guide bars, responsive to the strip shifting signal.

46. The apparatus of claim 45, wherein the guide bar position varying means comprising means for varying the angle of the guide bars to the longitudinal axis of the strip.

47. The apparatus of claim 45, wherein the guide bar positioning means comprises means for varying the distance between the first and second, and between the third and fourth, guide bars.

48. The apparatus of claim 1, wherein the strip shifting means comprises means for bendingly changing the plane of the strip a plurality of times adjacent to the first strip section thereby transversely shifting the position of the first strip segment an amount specified by the strip-shifting signal, and further bendingly changing the plane of the strip a plurality of times adjacent the first strip segment and on the side of the first section opposing that of the first plane changings, to restore the strip to its original position.

49. Apparatus for shifting a segment of an elongate flexible strip transversely with respect to its longitudinal axis, comprising:

a. a frame;

b. first and second guide bars and third and fourth guide bars comprising first and second guide bar pairs respectively, at least a portion of each guide bar being a convexly curved cylindrical surface;

c. first and second strip holders attached to the frame at spaced apart locations and adopted to grip the strip at spaced apart areas on the strip;

d. a first guide bar mount supporting the first pair of guide bars, and a second guide bar mount supporting the second guide bar pair, the guide bars comprising each pair being in spaced apart and substantially parallel relationship to each other, each mount being attached to the frame in a position such that when the strip is gripped by the holders, is passed between the first and second, and the third and fourth guide bars, is partially wrapped around the convex surface of each guide bar, and is drawn taut, the flat strip surfaces adjacent and external to the first pair of guide bars are substantially parallel and the flat strip surfaces adjacent and external to the second pair of guide bars are substantially parallel, and the guide bars are angled to the longitudinal axis of the strip causing a predetermined offset of the strip between the two pairs of guide bars.

50. The apparatus of claim 49, wherein each guide bar mount further comprises means for varying the angle of the guide bars supported thereby, to the longitudinal axis of the strip.

51. The apparatus of claim 49, wherein each guide bar support comprises means for varying the distance between the guide bars supported thereby.

52. The apparatus of claim 49, wherein each guide bar support comprises means for changing the position of the guide bar pairs relative to the frame. 

1. APPARATUS FOR ACCESSING WITH A DATA TRANSDUCER HAVING A TRANSCRIBING SURFACE, A LONGITUDINAL RECORDING TRACK ON AN ELONGATE FLEXIBLE RECORDING STRIP AND SPECIFIED BY A TRACK ADDRESS SIGNAL, COMPRISING: A. A FRAME; B. FIRST AND SECOND STRIP HOLDERS ATTACHED TO THE FRAME AT SPACED APART LOCATIONS AND HOLDING THE STRIP AT, RESPECTIVELY, FIRST AND SECOND AREAS ON THE STRIP BETWEEN WHICH IS LOCATED A FIRST STRIP SECTION HAVING AT LEAST TWO RECORDING TRACKS ON ITS SURFACE; C. TRANSDUCER HOLDING MEANS FOR MAINTAINING THE TRANSCRIBING SURFACE OF THE DATA TRANSDUCER WITHIN A PREDETERMINED DATA TRANSCRIBING DISTANCE OF THE FIRST STRIP SECTION AND MOVING THE TRANSDUCER RELATIVE TO THE FIRST STRIP SECTION IN A PATH HAVING A SHAPE SUBSTANTIALLY THE SAME AS THE RECORDING TRACKS; D. MEANS FOR SHIFTING ONLY THE FIRST STRIP SEGMENT, TRANSVERSELY TO THE RECORDING TRACKS ON IT, TO A POSITION WITH RESPECT TO THE TRANSDUCER SPECIFIED BY A STRIP SHIFTING SIGNAL; AND E. CONTROL MEANS RECEIVING THE TRACK ADDRESS SIGNAL, FOR DETERMINING THE STRIP POSITION PLACING THE TRACK SPECIFIED BY THE TRACK ADDRESS SIGNAL WITHIN THE PREDETERMINED DATA TRANSCRIBING DISTANCE OF THE TRANSCRIBING SURFACE OF THE TRANSDUCER, AND SUPPLYING A STRIP SHIFTING SIGNAL TO THE STRIP SHIFTING MEANS SPCIFYING THIS POSITION.
 2. The apparatus of claim 1 wherein the strip shifting means comprises: a. first through fourth guide bars at least a part of the exterior of each being a convexly curved cylindrical surface; b. a first adjustable guide bar support attached to the frame in a position holding the first and second guide bars against opposite strip surfaces between the transducer and the first holder with the convex surface of these two bars at least partially encircled by the strip, and forming the strip into second, third, and fourth flat sections tangent to the convex surface of the first, second, and both guide bars respectively, with the tangent lines of the fourth section with the first and second convex guide bar surfaces being parallel; c. a second adjustable guide bar support attached to the frame in a position holding the third and fourth guide bars against opposite strip surfaces between the transducer and the second holder with the convex surface of each bar at least partially encircled by the strip, and forming the strip into fifth, sixth and seventh flat sections tangent to the convex surfaces of the third, fourth and both guide bars respectively with the tangent lines of the seventh section with the third and fourth convex guide bar surfaces being parallel; and d. first and second means moving the first and second guide bar supports respectively and changing the positions of the guide bars relative to the transducer holding means for shifting the strip transversely with respect to the recording tracks thereon to the position specified by the strip position signal.
 3. The apparatus of claim 2 wherein the first and second guide bar supports include respectivEly first and second pivots attached to the frame and positioning the bars to make the second and fifth strip sections parallel respectively to the fourth and seventh strip sections and perpendicular respectively to the axes of rotation of the first and second pivots; and wherein the support moving means includes means for pivoting the first and second guide bar supports about their respective pivots.
 4. The apparatus of claim 3 wherein the guide bar support pivoting means further comprises means for pivoting the first and second guide bar supports substantially equal amounts.
 5. The apparatus of claim 3 wherein each support pivoting means further comprises a voice coil connected between the support and the frame.
 6. The apparatus of claim 3 wherein the first and second guide bar supports further comprise respectively first and second pivots attaching their respective supports to the frame at points between the ends of the bars held by each support, and wherein each support pivoting means comprises a pair of elements each having a pair of spaced apart control points whose distance apart varies responsive to the strip position signal, a control point of one element attached to its associated support with the other control point of each element attached to the frame.
 7. The apparatus of claim 6 wherein each element comprises a voice coil having one control point on the armature and the other on the field.
 8. The apparatus of claim 7 wherein the lever arms formed between each support pivot and the points of attachment of the element control points to it are equal; and wherein each pair of elements comprising a support pivoting means comprises positioning devices whose distance between control points varies equally responsive to identical strip position signals.
 9. The apparatus of claim 8 wherein each positioning device comprises a voice coil attached so as to substantially form a right angle with a line connecting the points of attachment of the voice coils to the support when the strip is approximately midway between its extreme positions.
 10. The apparatus of claim 6 wherein increase in the distance between the control points of each element comprising a support pivoting means urges the support to rotate in the same direction.
 11. The apparatus of claim 2 wherein the first and second guide support moving means each include respectively means for causing the distance between the first and second and the third and fourth bars to change maintaining meanwhile the specified geometric relationships, and further comprising means for attaching the guide bar supports to the frame in a position placing the lines of tangency formed by the fourth, and seventh strip sections at predetermined angles to a plane perpendicular to the drum axis, and placing the second and fifth strip sections parallel respectively to the third and sixth strip sections.
 12. The apparatus of claim 11 wherein the bar distance changing means further comprises means for maintaining the distances between the first and third, and second and fourth, guide bar substantially equal.
 13. The apparatus of claim 11 wherein the support attaching means further comprises means for attaching the guide bar supports so as to place the bars at substantially equal angles to the data track.
 14. The apparatus of claim 1 wherein the transducer holding means comprises a circular drum rotatably mounted on the frame and partially encircled by the first strip section, and having the transcribing surface of the data transducer embedded in and facing outwardly from its curved surface.
 15. The apparatus of claim 14 further comprising a. first and second idler bars, at least a part of the exterior of each being a convexly curved cylindrical surface; b. a first idler bar support attaching the first idler bar to the frame immediately adjacent the drum with the convex surface of the first idler bar at least partially encircled by the strip and the lines of tangency formed by the strip section between the fIrst idler bar and the drum substantially parallel; and c. a second idler bar support attaching the second idler bar to the frame immediately adjacent the drum on the side opposite that of the first idler bar with the convex surface of the second idler bar at least partially encircled by the strip and the lines of tangency formed by the strip section between the first idler bar and the drum substantially parallel.
 16. The apparatus of claim 14 including means for maintaining an air bearing interface between the strip and at least one surface with respect to which it slides.
 17. The apparatus of claim 16 wherein the air bearing means comprises a plurality of areas on the surface upon which the strip slides, each containing at least one aperture, and means for forcing air through the apertures.
 18. The apparatus of claim 17 wherein the aperture is located in the cylindrical surface approximately 5 degrees from a tangent line of the strip section and between the tangent lines.
 19. The apparatus of claim 1 wherein the strip holders include means for applying tension within a predetermined range between them to the first strip segment.
 20. The apparatus of claim 1 wherein the strip holders each further comprise means for maintaining equal tension across the width of the strip and total tension within a predetermined range in the strip.
 21. The apparatus of claim 20 wherein the equal tensioning means further comprises first and second clamps, each non-slippingly gripping one end of the strip across substantially its entire width and attached respectively to the first and second strip holders.
 22. The apparatus of claim 1 wherein the first and second strip holders comprise, respectively, first and second storage spools rotatably attached to the frame; and means receiving the track address signal, for rotating each spool to unwind a length of the strip from one spool and concurrently take up a similar length on the other spool, responsive to the track address signal.
 23. The apparatus of claim 22 wherein the storage spool rotating means further comprises means applying opposing torque to the spools for maintaining strip tension within predetermined limits.
 24. The apparatus of claim 22 further comprising third and fourth idler bars, at least a part of the surface of each having a convexly cylindrical shape and both attached to the frame, the cylindrical surface of the third always at least partially encircled by the strip portion immediately adjacent the second takeup spool, the tangent lines of each strip section between each idler bar and its associated storage spool being parallel and coplanar.
 25. The apparatus of claim 22 further comprising third and fourth idler bars, each having a partially convex cylindrical surface and each attached to the frame to allow the strip segments immediately adjacent the first and second storage spools to at least partially encircle the convex surfaces of the first and second idler bars respectively.
 26. The apparatus of claim 22 wherein the strip has a plurality of block markers at predetermined intervals, and wherein the track address signal includes a block address signal; wherein the spool rotating means further comprises means receiving a block location signal for taking up on one spool and unwinding on the other spool, a sufficient length of strip to position an addressed block to partially encircle the drum; and wherein the control means further comprises means sensing the current position of the strip for supplying a block location signal to the spool rotating means.
 27. The apparatus of claim 26 wherein the strip includes a plurality of unique block markers longitudinally spaced, and wherein the strip position sensing means includes a sensor identifying each marker as the strip is moved.
 28. The apparatus of claim 1 wherein the control means comprises: a. a strip position sensor, including a strip sensing element, attached to the frame, and supplying a strip position signal specifying The strip position; and b. a controller receiving the strip position signal and the track address signal, comparing them to determine the strip shifting signal to move the strip to the position for addressing the specified track, and supplying this strip shifting signal to the strip shifting means.
 29. The apparatus of claim 28 wherein the strip position sensor comprises a strip edge sensor.
 30. The apparatus of claim 28 wherein the strip position sensor comprises a strip edge sensor issuing a strip position signal specifying the position of the edge of the first strip segment.
 31. The apparatus of claim 28 wherein the strip position sensor includes a carrier movably attaching the sensing element to the frame and shifting the element in a path substantially parallel to the axis of the drum responsive to a sensor shifting signal, and supplying a signal specifying the position of the sensing element.
 32. The apparatus of claim 31 wherein the controller further comprises means for shifting the sensing element responsive to the track address signal to a position causing the strip position signal to have a predetermined value when the specified track is being addressed, and for supplying a strip shifting signal to the strip shifting means causing the strip to shift until the predetermined strip position signal value is reached.
 33. The apparatus of claim 31 wherein the strip position sensor comprises a pair of strip edge sensors each furnishing a strip position signal varying as the strip moves between a pair of predetermined positions relative to the edge sensors.
 34. The apparatus of claim 33 wherein each edge sensor comprises a photocell.
 35. The apparatus of claim 31 wherein the controller further comprises: a. means supplying a strip shifting signal to the strip shifting means responsive to the track address signal, for causing the strip to move laterally toward the position permitting addressing of the specified track by the head and to stop the lateral strip movement responsive to an accessing value of the sensor position signal; b. means issuing a sensor shifting signal for causing the sensor to shift with the strip to maintain the sensor near a preferred location relative to the strip responsive to the sensing element position signal; and c. wherein the strip position sensor includes means for supplying the accessing value of the sensor position signal to the controller when the strip approaches the specified position.
 36. The apparatus of claim 1 wherein the transducer holding means comprises a circular drum rotatably mounted on the frame and positioned to be partially encircled by the first strip section, and having the transcribing surface of the data transducer embedded in and facing outwardly from its curved surface, and wherein the strip shifting means comprises: a. first through fourth guide bars at least a part of the exterior of each being a convexly curved cylindrical surface; b. a first guide bar support movably attached to the frame and positioned to hold the first and second guide bars against opposite strip surfaces between the transducer and the first holder with the convex surface of each bar at least partially encircled by the strip, and forming the strip into second, third, and fourth flat sections tangent to the convex surfaces of the first, second, and both guide bars, respectively, with the tangent lines of the fourth section with the first and second guide bar convex surfaces being parallel; c. a second guide bar support movably attached to the frame and positioned to hold the third and fourth guide bars against opposite strip surfaces between the transducer and the second holder with the convex surface of each bar at least partially encircled by the strip, and forming the strip into fifth, sixth and seventh flat sections tangent to the convex surfaces of the third, fourth and both guide bars, respectively with the tangent lines of the seventh section with the third and fourth guide bar convEx surfaces being parallel; and d. first and second means moving the first and second guide bar supports respectively and changing the positions of the guide bars relative to the transducer holding means for shifting the strip transversely with respect to the recording tracks thereon to the position specified by the strip position signal.
 37. The apparatus of claim 36 wherein the first and second guide bar supports include respectively first and second support pivots attached to the frame and positioning the bars to make the second and fifth strip section parallel respectively to the third and sixth strip sections and perpendicular respectively to the axes of rotation of the first and second pivots; and wherein the support moving means includes means for pivoting the first and second guide bar supports to cause the first strip section to shift responsive to the strip position signal to a position relative to the transducer permitting the addressed track to be traversed by the transducer as it moves relative to the first strip section.
 38. The apparatus of claim 37 wherein the support pivoting means further comprises means for maintaining the axes of the bars supported by the first support at an angle measured clockwise from the axes to a plane perpendicular to the drum axes, equal to the angle measured counterclockwise from the axes of the bars supported by the second support, to the plane.
 39. The apparatus of claim 37 wherein the first and second strip holders comprise respectively, first and second storage spools rotatably attached to the frame and means receiving the track address signal, for rotating each spool to unwind a predetermined length of the strip from one spool and concurrently take up a similar length on the other spool, responsive to the track address signal; and to maintain a predetermined tension in the strip section between the taken-up lengths on the spools during transducing operations.
 40. The apparatus of claim 37 including a strip position sensor mounted on the frame and supplying a signal specifying the location of the first strip segment relative to the data transducer path to the strip position control means; and wherein the strip position control means further comprises a comparator receiving the track address signal and determining therefrom the transverse position of the strip permitting the data transducer to access the track, comparing the strip location to the strip location permitting track access, and issuing the strip position signal to the strip shifting means.
 41. The apparatus of claim 40 wherein the strip position sensor comprises a strip edge sensor issuing a strip edge position signal specifying the position of the edge of the first section relative to the data transducer path.
 42. The apparatus of claim 36 wherein at least one guide bar includes means for creating an air bearing contact between the strip portion encircling it and the guide bar.
 43. The apparatus of claim 42 wherein the air bearing creating means comprises a plurality of areas on the strip-encircled surface of the guide bar having orifices therein, and means for supplying compressed air to these orifices.
 44. The apparatus of claim 43 wherein at least one orifice is set approximately 5* from a tangent line of the strip with the guide bar and between the two tangent lines.
 45. The apparatus of claim 1 wherein the strip shifting means comprise: a. first and second guide bars and third and fourth guide bars, comprising first and second guide bar pairs respectively, at least a portion of each guide bar being a convexly curved cylindrical surface; and b. a first guide bar mount supporting the first pair of guide bars, and a second guide bar mount supporting the second pair of guide bars, the guide bars comprising each pair being in spaced apart and substantially parallel relationship to each other, each mount being attached to the frame in a position such that: when the strip is held by the holders, is passed between tHe first and second, and the third and fourth guide bars, is partially wrapped around the convex surface of each guide bar, and is drawn taut, the flat strip surfaces adjacent and external to the first pair of guide bars are substantially parallel, the flat strip surfaces adjacent and external to second pair of guide bars are substantially parallel, and the guide bars are angled to the longitudinal axis of the strip causing an offset of the strip between the two pairs of guide bars to change the offset of the strip between the two pairs of guide bars; and c. means receiving the strip shifting signal for varying the positions of the guide bars to change the offset of the strip between the pairs of guide bars, responsive to the strip shifting signal.
 46. The apparatus of claim 45, wherein the guide bar position varying means comprising means for varying the angle of the guide bars to the longitudinal axis of the strip.
 47. The apparatus of claim 45, wherein the guide bar positioning means comprises means for varying the distance between the first and second, and between the third and fourth, guide bars.
 48. The apparatus of claim 1, wherein the strip shifting means comprises means for bendingly changing the plane of the strip a plurality of times adjacent to the first strip section thereby transversely shifting the position of the first strip segment an amount specified by the strip-shifting signal, and further bendingly changing the plane of the strip a plurality of times adjacent the first strip segment and on the side of the first section opposing that of the first plane changings, to restore the strip to its original position.
 49. Apparatus for shifting a segment of an elongate flexible strip transversely with respect to its longitudinal axis, comprising: a. a frame; b. first and second guide bars and third and fourth guide bars comprising first and second guide bar pairs respectively, at least a portion of each guide bar being a convexly curved cylindrical surface; c. first and second strip holders attached to the frame at spaced apart locations and adopted to grip the strip at spaced apart areas on the strip; d. a first guide bar mount supporting the first pair of guide bars, and a second guide bar mount supporting the second guide bar pair, the guide bars comprising each pair being in spaced apart and substantially parallel relationship to each other, each mount being attached to the frame in a position such that when the strip is gripped by the holders, is passed between the first and second, and the third and fourth guide bars, is partially wrapped around the convex surface of each guide bar, and is drawn taut, the flat strip surfaces adjacent and external to the first pair of guide bars are substantially parallel and the flat strip surfaces adjacent and external to the second pair of guide bars are substantially parallel, and the guide bars are angled to the longitudinal axis of the strip causing a predetermined offset of the strip between the two pairs of guide bars.
 50. The apparatus of claim 49, wherein each guide bar mount further comprises means for varying the angle of the guide bars supported thereby, to the longitudinal axis of the strip.
 51. The apparatus of claim 49, wherein each guide bar support comprises means for varying the distance between the guide bars supported thereby.
 52. The apparatus of claim 49, wherein each guide bar support comprises means for changing the position of the guide bar pairs relative to the frame. 